Variable inductor



Oct. 25, 1966 R. LA ROSA VARIABLE INDUCTOR Filed Sept. ll, 1964 m KI Mn n FIG. l

IOo. I

FIG. 2

FIG. 3

United States Patent O 3,281,748 VARIABLE INDUCTOR Richard La Rosa, South Hempstead, N.Y., assignor to Hazeltne Research, Inc., a corporation of Illinois Filed Sept. 11, 1964, Ser. No. 395,813 11 Claims. (Cl. 336-139) The present invention relates to a novel type of variable in-ductor, which is particularly useful in conjunction with coaxial transmission lines.

Variable inductors, as such, are well known in the art and consist basically of an inductance, commonly in the form of a helical conductor, whose active length may be varied by addi-ng or eliminating turns of the coil to` correspondingly vary its inductance.

It is an object of the present invention to provide new and improved variable inductors which are simple, inexpensive, and highly reliable and inductors wherein their inductance may be varied by physical movement of an inductive device relative to a conductor feeding said device.

It is another object of the present invention to provide new and improved variable inductors which are particularly useful with coaxial transmission lines.

In accordance with the present invention, a variable inductor comprises a conductor which enters one end and comes out the other end of the variable inductor for supplying signals to and carrying signals from the Variable inductor, an inductive device coaxial with and electrically coupled to the conductor and movable relative to the conductor along the common axis, the inductive device having an inductance dependent on active length. The variable inductor also includes means electrically coupled to -the inductive device and lxed relative to the conductor for varying the active length of the inductive device, when the inductive device is moved along the common axis, to cause a corresponding variation in the inductance of the inductive device.

For a better understandin-g of the present i-nvention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing:

FIG. 1 is a cross-sectional drawing of one embodiment of the present invention;

FIG. 2 is a cross-sectional drawing of another embodiment of the present invention, and

FIG. 3 is a cross-sectional drawing of yet another embodiment of the present invention.

Description of the variable inductor of FIG. 1

In FIG. 1 of the drawing, there is shown a variable inductor embodying the present invention in one form. As shown, the variable inductor of FIG. 1 includes a conductor 10, which may be, for example, the center conductor of a coaxial transmission line. Also included in the variable inductor of FIG. 1 is an inductive device 11 which comprises a supporting form 12, a helical conductor 13 disposed on form 1-2, and rst coupling means 14 for coupling an end of helical con-ductor 13 to conductor 10. Inductive device 11 is coaxial with conductor 10 and movable relative to conductor along the axis which is common to inductive device 11 and conductor 10. Inductive device 11 has an inductance dependent on its active length, as will be described more fully hereinafter.

Also included in the variable inductor of FIG. 1 is the combination of second coupling means 15 disposed on support 16, which comprises means coupled to inductive device 11 and fixed relative to conductor 10A for varying the active length of inductive device =11, when device 11 is moved along the aforementioned common 3,281,748 Patented Oct. 25, 1966 ICC axis, to cause a corresponding variation in the inductance of inductive device 11.

The term active length, as used herein, refers to the length of inductive device 11 `between the permanently shorted end turn 17 of helical conductor 13 and that turn of helical conductor 13 which is coupled to sec-ond coupling means 15, as shown, for example, in FIG. 1.

Form 12 may be constructed of any conventional rigid insulating material, such as ceramic, glass, or plastic for example. While in FIG. 1 supporting form 12 is shown as being circular-cylindrical in shape, it is only shown as such to illustrate the principle of the present invention, and is not meant to limit variable inductors constructed in accordance with the present invention to that particular shape.

Helical conductor 13 is disposed -on supporting form 12 in a helical manner, wherein the pitch of the helix may be either uniform or nonuniform, depending on the variable inductance characteristic desired. Helical conductor 13 may take any suitable form, such as a conducting wire wound in a groove in supporting form l12, or a conducting ribbon bonded to form 12, or a conducting lm deposited on form 12 and then partially etched away to construct a helical conductor. Helical conductor 13 is shown in FIG. l as having a permanently short-circuited turn 17 at one end, the remaining end being opencircuited. It will -be obvious that the short-circuited turn 17 is not necessary, in which case lboth ends of helical conductor 13 may be made open-circuited.

Coupling means 14 may, as shown in FIG. 1, consist of one or more wiping contacts fastened to the end, which in the present case is short-circuited turn 17, of helical conductor 13 and being slidably coupled to conductor 10. Coupling means 14 may take other forms, such as, for example, a contacting sleeve or a noncontacting choke, both of which are well known in the art. Any other suitable coupling means which provides electrical coupling between conductor 10 and the end of helical conductor 13 while permitting inductive -device 11 to be moved along the aforementioned common axis, may be used with the present invention.

Second coupling means E15 and support 16 may take several different forms, depending upon whether the variable inductor is to sup-ply series or shunt inductance. In the exa-mple illustrated in FIG. "l, second coupling means 15 is shown constructed similarly to first coupling means 14, described hereinbefore. In this example, support 16 lmay be constructed of any conventional rigid insulating material, since it serves only to support second coupling means 15 in the relationship shown in FIG. 1. In the embodiment of FIG. 1, second coupling means 15 may be coupled, for example, to ground or to other circuits to provide shunt inductance. To provide series inductance, the embodiment of FIG. 2 may be used. As shown in FIG. 2, conductor 10 is -br-oken to form first and second segments 10a and 10b, respectively. The broken ends of conductor 10` may be supported, for example, lby an extension of support 16', as shown. In order to complete the series connection, second coupling means 15 may be extended as shown, so as to be jointly electrically coupled to inductive device -11 and the second seg ment 10b of conductor 10.

In the embodiments shown in FIGS. l and 2, inductive device 11 is moved along the common axis by sliding. In FIG. 3, another embodiment of the present invention is shown wherein the second coupling means consists of an electrically conductive member 18 having an aperture which is tapped to Imatch the pitch of helical conductor 13. Member 18 engages helical lconductor 13 in the same manner as a nut engages the threads of a bolt. In this case, inductive device 11 is moved along the common axis by screwing it into, or out of, conductive member 18. In

The operation of the variable inductors shown in FIGS. l 'and 2 will be readily apparent to those skilled in the art. However, as an example, a brief description of the method -of operation of the varia-bleinductor of FIG. 1 isset forth hereinbelow.

'As will be understood by those skilled in the art, helical conductor 13 has an inductance which is dependent upon its active length, as defined hereinbefore. In other words, the inductance of helical conductor 13 is directly related to the number of its coils which are coupled to conductor 10, or the number of coils between the permanently short-circuited coil 17 of helical conductor 13 and that coil of helical conductor 13 which is short-circuited by second -coupling means 15. As will be apparent from the embodiment illustrated in FIG. l, by moving inductive device 11 along the axis established by conductor the number of active turns, or the active length and, therefore, the inductance, of helical conductor 13 may be varied. Hence, in order to vary the inductance of the variable inductor shown in FIG. 1, all that is necessary is that the inductive device 11 be moved to the left in order to increase its inductance, or to the right in order to decrease its inductance. 11 may be accomplished through any suitable means, as will 'be apparent to those skilled in the art.

Thus there have been disclosed variable inductors which are simple and convenient in form and which provide accurately variable inductances without requiring elaborate and complex mechanical tuning arrangements.

While there have been described what are, at present, considered to be the preferred embodiments of the present invention, it w-ill be obvious to those skilled in the art that various changes and modifications may be made therein Without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A variable inductor comprising:

.a conductor which enters one end and comes out Iof the other end o f said variable inductor for supplying -signals to and carrying s-ignals from said variable inductor;

an inductive device coaxial with and coupled electrically to said conductor and movable relative to said conductor along the common axis, said inductive device having an inductance dependent on active length;

and means coupled to said inductive device and -fixed relative to said conductor for varying the active length of said inductive device, when said device is moved .along said common axis, to cause a corresponding l variation in the inductance of said inductive device.

2. A variable inductor as recited in claim 1 wherein said conductor is a continuous conductor and wherein the inductive device is slidably coupled to the conductor, and the means for varying the active length of said inductive device is slidably coupled to said inductive device.

3. A variable inductor comprising:

a continuous first conductor which enters one end and cornes out the other end of said variable inductor for supplying signals t-o and carrying signals from said variable inductor;

an inductive device, including a helical second conductor, coaxial with and electrically coupled to said first conductor, and movable relative to said first conductor along the common axis, said inductive device having an inductance dependent on active length;

and means electrically coupled to said inductive device and fixed relative to saidfirst conductor for varying The rnovment of inductive device the active length of said inductive device, when said` device is moved along said axis, to cause a corresponding variation in the inductance of said inductive device.

A variable inductor comprising:

continuous first conductor which enter-s one end and comes -out the other end of said variable inductor for supplying signals to and carrying signals from said variable inductor;

an inductive device, including a helical second conductor, coaxial with and electrically coupled to said first conductor, and movable relative to said first conductor, along the common axis, said inductive device having an inductance dependent on active length;

and means electrically coupled to said inductive device an inductive dvice, including a uniform-pitch helical second inductor, coaxial with said rst conductor and electrically coupled to said first conductor and movable relative to said first conductor along the common axis, said inductive device having an inductance dependent on active length;

and means, including :an electrically conductive member having an aperture which is ltapped to match the pitch of said helical conductor, said member being electrically coupled to said inductive device by threadably'engaging at least one turn of said helical second conductor, and being fixed relative to said first conductor, for varying the active length of said inductive device, when said second conductor is moved along said common axis by screwing said second conductor into or out of said conductive member, to cause a corresponding variation in the inductance of said inductive device.

A variable inductor comprising:

continuous first conductor which enters one end and cornes out the other end of said variable inductor for supplying signals to and carrying signals from said variable inductor;

an inductive device, including a helical second conductor, coaxial with and electrically coupled to said first conductor, and movable relative to said first conductor, along the common axis, said inductive device having an inductance dependent on active length;

and means, including a plurality of electrically common and means jointly coupled to said inductive device and the second segment of said conductor, and fixed rela-` A variable inductor comprising:

conductor which enters one end and comes out the other end of said variable inductor said conductor being broken intermediate its ends to form first and second segments for supplying signals to and carrying signals from said variable inductor;

'ari inductive device coaxial with said conductor and cou-- pled to the first segment of said conductor and movable relative to said conductor along the common axis, said inductive device having an inductance dependent on active length;

tive to said conductor, for varying the active length of said inductive device, when said device is moved along said common axis, to cause a corresponding variation in the inductance of said inductive device.

8. A variable inductor comprising:

a first conductor which enters one end and cornes out the other end of said variable inductor said conductor being broken intermediate its ends to form first and second segments for supplying signals to and carrying signals from said variable inductor;

an inductive device, including a helical second conductor, coaxial `with said first conductor and electrically coupled to the rst segment of said first conductor, and movable relative to said first conductor along the 'common axis, said inductive device having an inductance dependent on active length;

and means jointly electrically coupled to said inductive device and the second segment of said first conductor, and fixed relative to said first conductor for varying the active length of said inductive device, when said device is moved along said `common axis, to cause a corresponding variation in the inductance of said inductive device.

9. A variable inductor comprising:

a first conductor which enters one end and comes out the other end of said variable inductor said conductor being broken intermediate its ends to form first and second segments for supplying signals to and carrying signals from said variable inductor;

an inductive device, including a helical second conductor, coaxial with said first conductor and electrically coupled to the first segment of said first conductor, and movable relative to said first conductor along the common axis, said inductive device having an inductance dependent on active length;

and means electrically coupled to said inductive device by threadably engaging at least one turn of said helical second conductor, said means also being electrically `coupled to the second segment of said first conductor, and fixed relative to said first conductor for varying the active length of said inductive device, when said device is moved along said common axis by screwing said device into or out of said means, to cause a corresponding variation in the inductance of said inductive device.

10. A variable inductor comprising:

a first conductor which enters one end and cornes out the other end of said variable inductor said conductor being broken intermediate its ends to form first and second segments for supplying signals to and carrying signals from said variable inductor;

an inductive device, including a uniform-pitch helical second conductor, coaxial with said first conductor and electrically coupled to the first segment of said first conductor, and movable relative to said first conductor along the common axiss said inductive device having an inductance dependent on active length;

and means, including an electrically conduct-ive member having Vau aperture Which is tapped to match the pitch of said helical conductor, said member being electrically coupled to said inductive device by threadably engaging at least one turn of said helical second conductor, said member also being electrically coupled to the second segment of said first conductor, and being fixed relative to said first conductor, for varying the active length of said inductive device, when said second conductor is moved along said common axis Iby screwing said second conductor into or out of said conductive member, to cause a corresponding variation in lthe inductance of said inductive device.

11. A variable inductor comprising:

a first conductor which enters one end and comes out the other end of said variable inductor said conductor being broken intermediate its ends to form first and second segments for supplying signals -to and carrying signals from said variable inductor;

an'inductive device, including a helical second conductor, coaxial with said first conductor and coupled to the rst segment of said first cnoductor and movable relative to said first conductor along the com- -mon axis, .said inductive device having an inductance dependent on active length;

and means, including a plurality of electrically common wiping contacts, jointly coupled to said second conductor and the second segment of said first conductor and fixed relatively to said first conductor, for varying the active length of said inductive device, when said second conductor is moved along said common axis, to cause a corresponding variation in the inductance of said inductive device.

References Cited by the Examiner UNITED STATES PATENTS 1,0l2,209 12/1911 Lewis 338-176 X 1,861,052 5/1932 Dabilier 336-139 X 2,139,443 12/1938 Craymer 336-144 X 2,735,076 2/1956 Hudson 336-137 LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

D. I. BADER, Assistant Examiner. 

1. A VARIABLE INDUCTOR COMPRISING: A CONDUCTOR WHICH ENTERS ONE END AND COMES OUT OF THE OTHER END OF SAID VARIABLE INDUCTOR FOR SUPPLYING SIGNALS TO AND CARRYING SIGNALS FROM SAID VARIABLE INDUCTOR; AN INDUCTIVE DEVICE COAXIAL WITH AND COUPLED ELECTRICALLY TO SAID CONDUCTOR AND MOVABLE RELATIVE TO SAID CONDUCTOR ALONG THE COMMON AXIS, SAID INDUCTIVE DEVICE HAVING AN INDUCTANCE DEPENDENT ON ACTIVE LENGTH; AND MEANS COUPLED TO SAID INDUCTIVE DEVICE AND FIXED RELATIVE TO SAID CONDUCTOR FOR VARYING THE ACTIVE LENGTH OF SAID INDUCTIVE DEVICE, WHEN SAID DEVICE IS MOVED ALONG SAID COMMON AXIS, TO CAUSE A CORRESPONDING VARIATION IN THE INDUCTANCE OF SAID INDUCTIVE DEVICE. 